Beam angle control during ion beam implantation has emerged as one of the critical parameters possibly second only to dose control. Implantation that takes place through apertures in masks with high aspect ratios (i.e., depth vs. width) is sensitive to the angle of incidence of the ions impinging on the workpiece surface. It is important that the angular distribution of ions be as symmetrical as possible in order to produce uniform dose into all desired areas of the workpiece. Obtaining uniform angles of incidence dictate that the angular distribution of the ion beams be accurately measured and controlled. Additionally, it is desired that ion beam emittance in both the x and y directions be measured at the plane of the workpiece. Knowing the emittance of the ion beam at the plane of measurement allows one to predict the ion beam envelope at any point in the free drift region.
Ion beam intensity is a measure of the number of particles per unit time at a given location of the ion beam cross section. The ion beam emittance is a measure of the angular spread of the beam at that location.
It is desirable to know the ion beam intensity and ion beam emittance across the extent of the ion beam. If doping problems occur, the intensity and emittance profile of the beam can be used for diagnosing those problems. Additionally, this information is useful when tuning the ion beam to assure consistency between successive workpiece doping cycles.
It is desirable that ion beam profile information be readily available on an essentially “real time” basis so that technicians monitoring ion implanter performance can make adjustments based upon the ion beam profile. Rapid updating of beam profile information allows those adjustments to be made and the effect the adjustments have on the beam profile to be studied and re-evaluated.
Thus, it is desirable to provide a system for improved ion beam angle calibration and emittance measurement.